Kathleen, like Sally Florkiewicz in Program Four, worked with Fast Plants; however, where Sally used them to illustrate the plant life cycle to her third graders, Kathleen used them to demonstrate variation among plant populations to her sixth graders.

Kathleen explained that most of the setup for the lesson took place early in the year when she was showing her students how to do a controlled experiment. In that activity, she had each of her students care for six Fast Plants: two served as the controls, two had low doses of salt in their water, and the final two had high doses of salt in their water. Her students watered the plants using
graduated cylinders and measured and recorded the height, number of leaves, and number of flowers on each of the plants for a period of several weeks. “What was really interesting was they weren’t sure whether salt was doing anything because some kids’ high-salt plants were the tallest of their six,” Kathleen commented.

For the activity taped for Session 5, Kathleen’s students measured the heights of a group of plants they had been growing. They recorded the height of each plant on a magnet, and posted the magnets on a graph at the front of the board. In total, the class measured the heights of 166 plants, and, after graphing them, they calculated the average and range heights of the population. The
graph illustrated the wide variability in the population, and Kathleen asked her students to speculate on the cause of it: Was the range due to environmental or genetic causes? The class then considered the potential advantages and disadvantages of being a short or tall plant in the population, before discussing ways that the height of the population could change in future generations.

Kathleen’s students then calculated the average for just three plants, and then ten and twenty plants, to illustrate how misleading the data could be if the sample was too small. “We’d like to see at what point does the average reflect what we think is the true average,” explained Kathleen.

The goal was for her students to realize that they need to consider sample size as part of the scientific method. “In elementary school, when you’re trying to teach the general idea of an experiment, you must start off very simply,” said Kathleen, “but at some point, kids need to understand the importance of sample size.”

Kathleen added that an understanding of the scientific method in general, and of sample size in particular, encourages a healthy degree of skepticism in students about things they read in newspapers, claims for ads, etcetera – “If they don’t see that there’s a lot of good scientific method there, they will know not to take it for fact.”